The file you send to a 3D printing service bureau directly affects part quality, processing time, and whether the bureau can make intelligent decisions about your design. The wrong format — or a correctly formatted file poorly exported — adds hours of repair time to your job and can produce dimensional inaccuracies that are invisible until you receive the part. At Layer X in Ahmedabad we receive hundreds of files weekly. Here is what we recommend for each process and why.
STL (Standard Tessellation Language)
STL is the oldest and most universal 3D printing format — every slicer and AM machine accepts STL. It represents a surface as a mesh of triangular facets. The resolution of the STL mesh determines whether curved surfaces (cylinders, spheres, fillets) are smooth or faceted in the final print.
The common mistake: Exporting STL at too low a resolution ("coarse" or "medium" in most CAD tools). A 50 mm diameter cylinder exported at coarse quality has 36 facets — the printed cylinder will have visible flats at 10° intervals. At fine quality (1,000+ facets), the print is smooth.
Correct STL export settings: Chord tolerance ≤ 0.01 mm, angular tolerance ≤ 0.5°. In SolidWorks: File → Save As → STL → Options → Fine. In Fusion 360: 3D Print → Refinement: High or Custom. In FreeCAD: Mesh Design → Tessellation → Tolerance 0.01 mm.
When to use STL: FDM, SLA, SLS polymer prints where no further CAD editing is needed and the mesh quality is verified before export. Not recommended for DMLS where post-machining is planned.
STEP (Standard for the Exchange of Product Data)
STEP (AP214 or AP242 variants) preserves the exact mathematical surface definition from the CAD model — parametric curves, NURBS surfaces, exact cylinder radii — rather than approximating them as triangles. This means Layer X can re-tessellate the STEP model at optimal resolution for the specific process and can extract exact dimensions for CMM comparison without depending on STL mesh quality.
Layer X's recommended format for all metal (DMLS) orders. STEP allows us to identify design intent, check for non-manifold geometry, add machining stock precisely to specified surfaces, and prepare for hybrid print-then-machine workflows. For SLS and FDM, STEP is also preferred when the part has curved surfaces or tight tolerances.
Send STEP AP214 (most compatible) or STEP AP242. Your CAD file → Save As → STEP file.
OBJ (Wavefront Object)
OBJ is a mesh format (like STL) with the addition of surface colour and texture data. It is primarily used for multi-colour printing (Bambu Lab AMS, Polyjet, or colour SLS) where colour mapping from the original CAD or 3D scan needs to be preserved. For monochrome functional engineering printing, OBJ offers no advantage over STL and is marginally more complex to process.
When to use OBJ: Multi-colour FDM printing with colour texture maps; architectural and artistic models; coloured product appearance models.
AMF (Additive Manufacturing File Format)
AMF is the official ISO/ASTM standard replacement for STL, designed specifically for 3D printing. It supports curved surface representation (unlike STL's flat triangles), multiple materials, colour, and metadata. Despite being technically superior to STL, AMF adoption is slow — not all slicers support it. For current commercial 3D printing, STEP remains a better choice than AMF for engineering work.
3MF (3D Manufacturing Format)
3MF is a Microsoft/industry consortium format that packages geometry, print settings, colour, and material data in a single file. It is natively supported by Bambu Studio, PrusaSlicer, and most consumer-grade slicers. For FDM orders with specific print settings embedded, 3MF is useful — but it is not appropriate for DMLS or SLS where the bureau determines process parameters, not the customer.
Format Selection Summary
| Process | Best format | Acceptable alternative |
|---|---|---|
| FDM (polymer) | STEP | STL (fine quality) |
| SLA (resin) | STEP or STL (fine) | STL (fine quality) |
| SLS (nylon) | STEP | STL (fine quality) |
| DMLS (metal) | STEP (required) | STL high-quality if no machining |
| Multi-colour FDM | OBJ or 3MF with colour | — |
Layer X accepts STEP, STL, OBJ, and 3MF. STEP is strongly preferred for all metal and precision polymer work. Submit your files and our engineering team will flag any format or mesh quality issues as part of the DfAM review before quoting.